The invention relates to non-ferrous metallurgy and is used for refining such molten metals as tin, lead, bismuth, zinc, and aluminum alloys from solid impurities, as well as for removing solid impurities from molten sulfur.
Known in the art are pyrometallurgical methods and apparatus for refining molten metals from insoluble impurities. These methods are based on gravity segregation, with the solid particles floating to the surface wherefrom they are skimmed. For example, tin is separated from iron by segregation after admixing carbon. Arsenic is separated from tin in the form of an aluminum compound insoluble in tin. Lead is refined from copper by segregation of copper sulfides, with the melt being treated with elementary sulfur.
In the case of segregational removal of insoluble impurities, a significant amount of the metal to be refined is removed together with the skimmings, thus reducing the direct extraction of the product. In this connection, filtrational methods of metal refinement have been suggested. For example, known in practice is a method of filtrating molten sulfur from solid arsenic compounds by a ceramal filter under vacuum.
Also known are a method and an apparatus for centrifugal filtration of metals. In this apparatus, the crude metal is poured into a rotating filter and is filtered off through slits provided in the periphery of the filter. The refined metal spills down the metal receiver and the solid particles are arrested at the slits. The centrifugal filtration of metal in such an apparatus enables the separation of the insoluble impurities with a lesser loss of the base metal with the skimmings as compared to the ordinary segregational methods.
However, the method and apparatus for centrifugal filtration of melts have the following disadvantages:
It is difficult to maintain the specified temperature of the filter casing and of the starting melt.
The solid particles floating to the surface of the starting melt are not uniformly poured into the apparatus, thus complicating its operation.
In the beginning of each filtration cycle, while the filter is not yet clogged with the solid sediment, the fine particles of the impurities penetrate through the filter slits and pass into the product. As the slits are being clogged, the product purity rises. Thus, the purity of the product metal is not uniform within one cycle and over the whole period of refinement.
During the operation of the apparatus, air is sucked into the rotating filter together with the metal flow which intensifies metal oxidation.
These disadvantages are caused by the fact that the filter is separated from the bulk of the metal which is fed for filtration in batches or in a flow with a varying content of the segregating impurities.